Furnace



FIG. 1 is a front elevational view of a furnace showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a side elevational view thereof taken from the left of FIG. 1, the side elevational view taken from the right of FIG. 1 being the mirror image thereof;

FIG. 4 is a rear elevational view thereof; and

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a furnace, as shown and described. 